It is desirable in certain reciprocating mechanisms, such as multiple cylinder internal combustion engines or reciprocating compressors, to utilize two or more pistons reciprocating in cylinders oriented in a substantially bilaterally opposed relationship to one another on either side of a crankshaft. Such an arrangement results in a compact, flat mechanism that is well suited for mounting under the floor of a vehicle, for example.
In prior opposed piston mechanisms, however, it has not been possible to have the cylinders be truly opposed to one another due to limitations in the manner in which connecting rods used for imparting reciprocating motion to the pistons are constructed.
As shown in FIG. 1, the connecting rod apparatus 10 for a typical opposed piston mechanism includes a crankshaft 12 defining an axis of rotation 14 and one or more rod journals 16 eccentrically mounted for circular rotation about the axis 14. A pair of connecting rods 18 are attached at one end to each rod journal 16, and extend in opposite directions from the crankshaft 12, for imparting reciprocating motion, through a piston pin connection 20 at the outer end of the connecting rods 18.
As shown in FIG. 2, the connecting rods 18 include a shank 22 extending between the piston pin connection 20 and a connecting rod eye portion 24. The connecting rod eye portion 24 is formed by a bearing saddle 26 attached integrally to the shank 22, and a bearing cap 28 that is bolted to the bearing saddle 26 so that the cap 28 can be removed for attaching the connecting rod 18 to the rod journal 16. The bearing saddle 26 and bearing cap 28 each include a semi-circular cylindrical surface 30 for receiving half of an insert bearing 32 disposed between the connecting rod 18 and the rod journal 16.
As shown in FIG. 1, when the connecting rods 18 are attached to the rod journal 16, they must be attached one behind the other on the rod journal 16, so that they can articulate with respect to one another on the rod journal 16 as the rod journal 16 travels in its circular path, because the connecting rod eye portion 24 extends completely around the rod journal 16. As a result, each member of the pair of connecting rods 18 attached to the same journal 16 reciprocates in a separate plane 34, 36 extending perpendicularly through the rod journal 16, and separated by an axial distance 38 from one another.
The necessity for having the axial distance 38 between the connecting rods 18 causes the connecting rod apparatus 10 to be longer than it could be if the connecting rods 18 could be attached to the rod journal 16 in a manner that would allow them to reciprocate bi-laterally in a common plane extending perpendicularly through the rod journal 16. This additional length is undesirable for a number of reasons, including making the apparatus 10 less compact and heavier than it would otherwise need to be. Also, having the connecting rods 18 introduces undesirable dynamic forces into the apparatus 10 that require the addition of extra counter weights on the crankshaft 12, and complex mounting devices to damp out vibrations resulting from the undesirable dynamic forces.
What is needed, therefore, is an improved connecting rod apparatus having connecting rods capable of bi-lateral reciprocating motion in a common plane extending perpendicularly through a rod journal on a crankshaft.